The present invention relates to a compressor to be driven by a motor, and, more particularly, to a compressor provided with a vibration reducing device which can reduce the vibration caused by the load torque fluctuation of the compressor.
Generally, in a rotary compressor, the motion balance is almost completely governed to remove the usual vibrations caused by the load torque fluctuations. Namely, the rotary portion of the rotary compressor is varied in rotation by the variations in load torque so that the twisting oscillations are caused in the compressor by the reaction force of the rotation variation. Accordingly, once the type of rotary compressor and load torque variation pattern for the compressor are determined, twist oscillations which may be almost constant are formulated to be caused in accordance with the determination.
Conventionally, as a measure for reducing the oscillations which are caused by such load torque changes, a dynamic oscillation absorber is additionally provided on the compressor container as disclosed in, for example, Japanese Patent Publication (unexamined) Tokkaisho No. 59-50244. The primary natural oscillation number of the dynamic oscillation absorber is made almost consistent with the rotation frequency or power supply frequency of the compressor to absorb the oscillations which are caused by the load torque changes. Also, it is known that the inertia movement of the rotation portion of the rotary compressor is made larger to render the rotary change of the rotation portion smaller, thereby reducing the oscillations which are caused by the load torque changes.
However, any one of the conventional art devices are not effective measures with respect to the oscillations which are caused by the load torque changes, because they are restrictive in their oscillation reduction, and therefore ineffective for oscillation reduction.
In order to check the oscillations caused by the load torque changes, the present inventor investigates the movement of the rotation portion of the rotary compressor. The movement with respect to the amplitude of a twisting vibration of the compressor in a direction of the rotary shaft thereof will be described by the following equation. EQU Is.multidot.(d.sup.2 .theta.s/dt.sup.2)+Ks.multidot..theta.s=T.sub.M -T.sub.L (i)
wherein
Is: inertia movement in a direction of the rotary shaft except for the rotation portion of the compressor PA0 .theta.s: rotary angle with respect to the amplitude of twisting vibration in a direction of the rotary shaft of the compressor PA0 Ks: spring constant of the support portion for the compressor in a direction of the rotary shaft PA0 T.sub.M : production torque of the motor PA0 T.sub.L : load torque of the compressor PA0 Ir: inertia movement of the rotation portion in the direction of the rotary shaft, PA0 .omega.r: angular velocity of the rotational portion of the compressor
In equation (i), to render the rotation changes of the rotation portion smaller through the smaller value of the right side with the change of the load torque T.sub.L of the compressor as the assumption, it is required to change the motor production torque T.sub.M in accordance with the changes in the load torque T.sub.L.
Also, the movement with respect to the rotation fluctuation of the rotation portion of the compressor including the rotor of motor and the crank shaft and rotor of compressor will be described by the following equation. EQU Ir(d.omega.r/dt)=T.sub.M -T.sub.L (ii)
wherein
In equation (ii), it is clearly understood that the rotational fluctuation of the rotation portion of the compressor is caused by the difference between the generating torque T.sub.M of the motor and the load torque T.sub.L of the compressor.
However, for instance, as the sliding operation is performed between the electric rotation angle and mechanical rotation angle in the case of the induction motor, it is difficult to control the timing to change the motor production torque T.sub.M as the power supply in accordance with the changes in the load torque T.sub.L, but it is possible to control the motor production torque T.sub.M if the power supply frequency is controlled minutely during one rotation by attaching some means to detect the mechanical rotation angle. Furthermore, in the case of the rotary compressor provided with the DC motor of the brushless type to be controlled by the inverter, the rotating position of the induction motor is almost located by the position detector so that it is possible to synchronize the changes in the motor production torque T.sub.M with the changes in the load torque T.sub.L.